Coin testing apparatus

ABSTRACT

Apparatus for distinguishing between genuine and spurious coins. The coin being tested is used to form a mechanical filter and driven to generate a mechanical oscillation inherent in the coin, which oscillation is then converted to an electrical signal having a frequency of the natural oscillation of the coin. The output of the mechanical filter is applied to a positive feedback oscillation generator for producing an oscillation signal output of a single mode, which oscillation signal output is in turn compared with a predetermined threshold for producing an output for indication of the genuiness or spuriousness of the coin.

United States Patent Miyazawa 1 Aug. 26, 1975 1 COIN TESTING APPARATUS[75] Inventor: Kuniaki Miyazawa, Tokyo, Japan Primary Examutler AnenKnowles I Assistant Exammer-H. Grant Skaggs [73] Assigneez Mitam ShopCo., Ltd., Fukul Attorney, Agent, or Firm-Hall & Myers Japan [22] Filed:Apr. 11, 1973 21 Appl. No.1 350,041

[52] US. Cl. 194/100 R; 73/672 [51] Int. Cl. G071 3/02 [58] Field ofSearch 194/100, 97, 99; 73/672; 209/1 1 1.9

[56] References Cited UNITED STATES PATENTS 2,576,423 11/1951 Stewart73/672 2,675,698 4/1954 Johnson 73/672 3,394,587 7/1968 Freeman 73/6723,438,493 4/1969 Goblc v 73/672 3,641,550 2/1972 Lynas et a1. 73/672FOREIGN PATENTS OR APPLICATIONS 2,017,390 10/1971 Germany 194/100 [57]ABSTRACT Apparatus for distinguishing between genuine and spuriouscoins. The coin being tested is used to form a mechanical filter anddriven to generate a mechanical oscillation inherent in the coin, whichoscillation is then converted to an electrical signal having a frequencyof the natural oscillation of the coin. The output of the mechanicalfilter is applied to a positive feedback oscillation generator forproducing an oscillation signal output of a single mode, whichoscillation signal output is in turn compared with a predeterminedthreshold for producing an output for indication of the genuiness orspuriousness of the coin.

4 Claims, 2 Drawing Figures COIN TESTING APPARATUS This inventionrelates to coin testing apparatus and;

more particularly to electrical apparatus for detecting spurious orcounterfeit coins.

Modern development of automats, automatic vending machines, automaticcoinexchangers, etc. requires consistent and reliable apparatus to testcoins, accepting only genuine coinsand rejecting all spuriousones.

According to conventional coin testing apparatus, spurious orcounterfeit coins are detected by measuring their outer dimensions andweight. In the method of detecting a spurious coin from agenuine one, amachine cannot select coins when they are identical in size withstandard genuine coins. In the weight-detecting method, a machine cannotsort out genuine coins from spurious coins when they areidentical inweight. Thus, automats are conventionally provided with a coin selectoroperable both by theouter dimension and weight of coins. However, in theweight-detecting method it is difficult to increase the rate ofselection without lowering the accuracy of detection. Moreover, if aspurious coin is intentionallyand deftly manufactured so as to providean identical size and weight with a standard genuine coin, the machinecannot distinguish one coin from the other.

SUMMARY OF THE INVENTION This invention is, therefore, directed to anovel apparatus for detecting spurious or counterfeit coins even if theyare manufactured identical to genuine coins in size and weight.

The present invention is based on the consideration of the fact that aphysical solid located in a free space has a natural oscillation in amedium. When an acoustical oscillation is propagated througha medium asa longitudinal wave or transversal wave, the rate of propagation isrepresented by a function of the density, Youngs modulus, Poissonsratio. etc. inherent in the material. Density is a physical quantitywhich derived from the outer dimensions and weight of the material,while Youngs modulus and Poissons ratio are physical amounts whichrelate to the quality of a body in acoustic propagation. Therefore, themeasurement of the specific resonance frequency depending on suchphysical quantity or amount is advantageously used to detect coins withhigh accuracy of selection.

This invention utilizes the fact that a coin has its specificoscillation frequency. As a standard has a typical outer dimensions anda fixed density of material, therefore its natural oscillation isregularized. Thus, it has a steep characteristic of resonance for thedrive by the natural oscillation. When a shock is given to a coin in afree space, it oscillates with several modes but produces a specificsound wave containing the natural oscillation. The natural oscillationis determined by the outer dimensions, weight and density of material ofthe coin. Thus, the measurement of the natural oscillation may detect aparticular coin from others.

According to the present invention, coin testing apparatus comprises amechanical filter which includes in its circuit a coin being detected.The steep characteristic of selection of the mechanical filter isutilized to provide a feedback amplification oscillation. Theoscillation signal of the mechanical oscillation frequency of a givencoin is selected by frequency through a resonant circuit and produces'anoutput signal of a single mode for the selection of a different coin.

- BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENT The mechanical filterincludes a coin 1 being detected, aspeaker 2 and a pressure sensor 3 disposed oppositely with respect tothe coin. When the speaker 2 is driven by application of acousticoscillation, the coin 1 can oscillate only if it is driven by themechanical resonance frequency inherent in the coin, but the coin willoscillate only slightly with another driving frequency. Namely, the coin1 has a steep characteristic of wave filter, allowing its own frequencyonly to pass therethrough from the driving acoustic frequencies.

The pressure sensor 3 receives the sound pressure of the mechanicalresonance oscillation of the coin 1 and acts as a sound pressuremicrophone or a soundelectricity transducer which converts the soundpressure to an electrical signal.

The output of the sensor 3 is an electrical signal having a frequency ofthe natural oscillation of the coin l and it can consist of a high Qmechanical filter having a steep resonancecurvea The output signal ofpressure sensor 3 is applied to an amplifier 4 for positive feedbackamplification of this feedback circuit. Then the circuit will oscillateat the resonance frequency of the coin 1.

In FIG. 2 the numeral 5 represents the mechanical filter consisting ofthe coin 1, speaker 2 and sensor 3 as shown in FIG. 1. The numeral 6represents the amplifier 4 of FIG. 1.

The output of mechanical filter 5, which includes the coin beingdetected, is amplified by the amplifier 6 and is fed back to themechanical filter 5 through a phase shifter circuit 7, a limiter 8, anda selector circuit 9. The closed loop of the blocks 5-6-7-8-9-5 in FIG.2 composes the feedback amplification generator described with referenceto FIG. 1.

The phase shifter circuit 7 functions to carry out phase shifting sothat the feedback amplification generator performs the positive feedbackwith a correct phase shift. The limiter 8 is to adjust the amplitude toa predetermined level so that the output level will not change inaccordance with a difference in the oscillation level.

The selector circuit 9 forms a L-C resonance circuit and determines theQ according to the selective characteristic of the coin so that it mayprovide a frequency characteristic having a wave form suitable for theselection by frequency. This wave is a pulse having steep leading andtrailing edges or blanks, but it has a somewhat round topmountain-shaped curve at the peak value for allowing a predeterminedsmall range of possibility against minute difference and selectiveerrors due to a fine scratch or a slight deformation of genuine coins.Such small range of possibility may be set in a predetermined range bythe designof L-C circuit. Thus it may be avoided that genuine coins areerrorneously rejected.

A part of the output of selector circuit 9 of FIG. 2 is fed back to themechanical filter Sand a part is also fed to a rectifier circuit 10 forconversion to a DC level, which, in turn, is applied to a comparator 11.

The comparator 11 is set to a predetermined threshold and functions toswitch the output signal from the selector circuit 9 to the ON or OFFstate in comparison with the threshold level. ON state is set, forexample, to detect and accept genuine coins, while OFF is set for thedetection of spurious coins for rejection thereof.

As explained above, the present invention utilizes the mechanicalresonance inherent in a coin for insertion thereof into a feedbackcircuit of a feedback amplification generator so that the generator maybe continuously oscillated.

A coin provides several modes of oscillation such as its thicknessoscillation, bent oscillation and unevenness oscillation, and besides,producing their compounding oscillations and other various oscillations.When a coin is hit by a hammer to produce oscillation, such variousmodes of oscillation are generated.

According to the present invention, the frequency selector circuit 9functions to readily pick up a specific single mode of oscillationsignal from the various modes of oscillation. Thus, the picked-up signalis selected by frequency to electrically determine the genuiness of agiven coin.

I claim: 7

1. Coin testing apparatus for distinguishing coins of a given type fromother coins, comprising, in combination, means including a speaker and acoin vibration sensor adapted to receive a coin to be tested betweenthem thereby forming a mechanical filter; said speaker being positionedto direct its output toward a face of the coin to produce mechanicalvibration of the coin; said coin vibration sensor being positioned torespond to vibrations of a face of the coin; said coin vibration sensorincluding means for producing an electrical output signal whosefrequency varies according to the frequency of vibration of the coin;selector means tuned to pass a frequency conforming to a naturalresonant frequency of a coin of said given type and attenuatefrequencies conforming to the natural resonant frequencies of othercoins; feedback means connecting said pressure sensor, said selectormeans, and said speaker in series, so that feedback means forms a closedloop in which the electrical signals generated in said loop as a resultof resonant vibrations of a coin of said given type will pass throughsaid selector means and provide feedback from said sensor to drive saidspeaker and thus build up the signal strength in said closed loop, andin which the electrical signals generated in said loop as a result ofresonant vibrations of a coin of another type will be attenuated by saidselector means; and output means connected to the output of saidselector means for giving a given output signal when the signals in saidclosed loop build up in response to vibrations from a coin of said giventype.

2. Coin testing apparatus as defined in claim 1 in which said feedbackmeans includes phase shifting means in said closed loop to provide aphase shift that will improve the build up of the signals resulting fromnatural vibrations of said given type of coin.

3. Coin testing apparatus as defined in claim 1 in which said feedbackmeans includes an amplifier in said closed loop.

4. Coin testing apparatus as defined in claim 3 in which said feedbackmeans also includes phase shifting means in said closed loop to providea phase shift that will improve the build up of the signals resultingfrom natural vibrations of said given type of coin, said closed loopalso including a limiter for limiting the amplitude of the signals insaid closed loop.

1. Coin testing apparatus for distinguishing coins of a given type fromother coins, comprising, in combination, means including a speaker and acoin vibration sensor adapted to receive a coin to be tested betweenthem thereby forming a mechanical filter; said speaker being positionedto direct its output toward a face of the coin to produce mechanicalvibration of the coin; said coin vibration sensor being positioned torespond to vibrations of a face of the coin; said coin vibration sensorincluding means for producing an electrical output signal whosefrequency varies according to the frequency of vibration of the coin;selector means tuned to pass a frequency conforming to a naturalresonant frequency of a coin of said given type and attenuatefrequencies conforming to the natural resonant frequencies of othercoins; feedback means connecting said pressure sensor, said selectormeans, and said speaker in series, so that feedback means forms a closedloop in which the electrical signals generated in said loop as a resultof resonant vibrations of a coin of said given type will pass throughsaid selector means and provide feedback from said sensor to drive saidspeaker and thus build up the signal strength in said closed loop, andin which the electrical signals generated in said loop as a result ofresonant vibrations of a coin of another type will be attenuated by saidselector means; and output means connected to the output of saidselector means for giving a given output signal when the signals in saidclosed loop build up in response to vibrations from a coin of said giventype.
 2. Coin testing apparatus as defined in claim 1 in which saidfeedback means includes phase shifting means in said closed loop toprovide a phase shift that will improve the build up of the signalsresulting from natural vibrations of said given type of coin.
 3. Cointesting apparatus as defined in claim 1 in which said feedback meansincludes an amplifier in said closed loop.
 4. Coin testing apparatus asdefined in claim 3 in which said feedback means also includes phaseshifting means in said closed loop to provide a phase shift that willimprove the build up of the signals resulting from natural vibrations ofsaid given type of coin, said closed loop also including a limiter forlimiting the amplitude of the signals in said closed loop.